This invention relates to polyvinyl acetate emulsion adhesives and in particular to such adhesive that are readily redispersible in both hot and cold water when dried in film form.
Polyvinyl acetate emulsions are commonly used in making multi-purpose adhesives; that is, adhesives which can be used to adhere such substrates as wood, paper, cloth, plastic and the like. Because such polyvinyl acetate has a glass transition temperature (Tg) at about room temperature, the acetate particles will coalesce to form a water resistant dry film at ambient temperature. This coalescence is made more extensive by the water-immiscible plasticizers for the acetate that are used in order to impart flexibility to the dry film. When such adhesive dries on a surface from which it is desired to remote it, it cannot be readily washed off with water or with water and soap solutions. In fact, if hot water is used, the polyvinyl acetate coalesces irreversibly to form an even more water-resistant film. Consequently, solvents for polyvinyl acetate are employed for the purpose of removal of the film.
For many uses, washability of such polyvinyl acetate adhesives in water is desired, particularly because of the fact that in their use, as by young children, the adhesives are often inadvertently deposited on clothing, tablecloths, carpets and other surfaces. Since solvents must be used, the surface from which the film is to be removed is often damaged or discolored by the solvent. Furthermore, the use of a solvent brings with it the hazards of fire and toxicity. It has long been desired to retain the excellent all-purpose adhesive properties of polyvinyl acetate adhesives, while at the same time eliminating the need for solvent to remove the film from surfaces onto which the film is deposited.
U.S. Pat. No. 3,442,845 of Columbus, et al, teaches a composition that imparts the needed redispersibility to the dried adhesive film in cold or hot water without affecting the general purpose adhesive properties of the polyvinyl acetate adhesive.
While the composition of the Columbus, et al, patent provides good adhesion to most substrates and has good water redispersibility, it lacks good adhesion to many plastics. As the water redispersible adhesives are used widely by small children who work with plastic film and plastic substrates in arts and crafts work, it is important that the adhesive they use adhere well to plastics. Being able to make things with plastics gives a child a sense of accomplishment. If the adhesive fails, it results in frustration to the child.